The invention relates to the improvements in the field of air pollution control, specifically for removal of ash particulate matter (PM), nitrogen oxides (NOx), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrocarbons (HC), carbon monoxide (CO) and other toxic air pollutants (such as, for example, Mercury) from the exhaust of fossil fuel burning boilers and furnaces. Particles emitted from fossil fuel boilers and furnaces range from very large (such as hundreds of microns) to very small (in most cases smaller than 1 micron, comparable in size with bacteria and 100 times smaller than human hair).
Also, depending on the type of the fuel and type of boiler or furnace being used, the exhaust gases will contain, most, if not all, of the following gas pollutants: Sulfur oxides (SOx) (mixed oxides of sulfur), Nitrogen oxides (NOx) (mixed oxides of nitrogen), Carbon Monoxide (CO) and others.
The field of cleaning gas pollutants from exhaust gases has been substantially urged forward with the passage of various Environmental Protection initiatives since the 1970s. One method that has evolved over the last 40 years includes selective catalytic nitrogen oxides reduction, which relies on catalytic reactions to reduce the nitrogen oxides to N2 gas and suffers from being expensive and subject to catalyst poisoning (which renders the catalyst ineffective). Similar processes have been constructed to deal with sulfur oxides. Another method is the selective non-catalytic reduction method, which relies on chemical reactions to reduce the nitrogen oxides to N2 gas. The non-catalytic methods require quite high temperatures and large volumes of reactor spaces to obtain the reductions desired. These demands, among others, make the non-catalytic chemical methods undesirable in many instances and simply not possible in other contexts.
One issue with the reduction methods above is that there are often incomplete reductions leaving some of the mixed oxides in the effluent gas. To deal with such leftover oxides, the art has coupled the above with aqueous scrubbers in which the gas containing the various mixed oxides is contacted with water. While higher oxides are reasonably soluble in water (forming acids), the lower oxide of nitrogen, nitrogen oxide (NO), and others have a very limited solubility in water, making the water scrubbing of gas exhaust (either before or after the reduction processes above) of limited value, especially as the environmental regulatory environment gets stricter.
Another process that has been developed in the art is to oxidize the gas flow so as to oxidize the mixed nitrogen oxides (NOx) and the mixed sulfur oxides (SOx) to the higher, more soluble oxides, which can then be subjected to a water scrubbing and thereby reduce the gas effluent content of these contaminants.
A persistent problem with all of the above processes however is dealing with ash that is in the sub-micron particle size, and which may still be contained in the effluent gas that is otherwise released to the environment. Environmental regulations of Mar. 16, 2012 place greater emphasis on the abatement of PM 2.5 particulates (all particles that are smaller than 2.5 microns) as well as on removal of mercury. While various designs of wet scrubber systems are suitable for collection of larger particulate sizes, high efficiency removal of sub-micron particles in typical wet scrubbers in the art rely on extraordinary amounts of energy being applied to the gas stream, resulting in prohibitive operating costs.
One process involving oxidation is to contact the gas stream with ozone. However, traditional ozone generators require either purified oxygen gas or “clean air” as inputs for the ozone generation, each of which is a substantial and costly disincentive to using those methods. In addition, the internal tubes in which the ozone is generated are made of glass, such that the ozone generator itself as a unit is fragile and subject to breakage in use, requiring still further costs in operation of the process. Oxidizing gas stream purification apparatus and methods known in the art include the following, non-limiting list of patents: U.S. Pat. Nos. 8,574,521; 7,514,053 (using non-ozone, non-free radical, chemical oxidation); and U.S. Pat. Nos. 7,303,735, 7,214,356, 7,052,662 and 9,533,311 (each using a separate ozone generator which then injects the ozone into the gas stream); among others. Each of these US patents is incorporated herein in their entirety by reference except to the extent that they contradict or detract from the statements made in the present application, in which case, the statements in the present application will control.